,,陡槽水力計算———參考《中小型水庫設(shè)計》中冊,,,,,,

一已知條件,,,,,,,,

設(shè)計流量(m3/s),,Q=,60,"溝槽后接以漸變段,其底坡為",,,0.050,

溝槽內(nèi)水深(m),,H=,1.5,"漸變段后為陡槽,首末端落差P=",,,12.000,

溝槽寬度(m),,B=,16,陡槽底坡為,,i=,0.125,

"混凝土襯砌,糙率",,n=,0.017,初選陡槽底寬(m)b=,,,8.000,

,,,,初選陡槽邊坡系數(shù)m=,,,1.000,

,以下進行水面曲線計算:,,,,,,,

(一)漸變槽計算,,,,,,,,

1漸變槽長度,,,,,,,,

取漸變收縮角θ0=,,30,由公式L=B-b/2tgθ/2(m)求得L=,,,,15,

2漸變段的臨界坡度ik及首端水深h1,,,,,,,,

單寬流量q=,,3.75,m3/s/m,臨界水深hk=,,1.16,(m),

,其相應(yīng)水力要素為,,,,,,,

,ωk=,18.62,,,χk=,18.33,,

,Rk=,1.016,,,Ck=,59.0,,

,ik=,0.0029,＜,0.050,故屬陡坡，,則漸變段首端水深取,,

,,,,為臨界水深，h1=hk=,,1.16,(m),

3漸變槽末端水深h2,,,,,,,,

,由公式Э1+iL=Э2+hf,,,,,,,

,首端斷面能量Э1求之如下：,,,,,,,

,Э1=,1.746,,首末兩端的落差為il=,,0.75,(m),

為求Э2和沿途損失能量hf，先假定h2=,,,,1.652,(m),末端斷面為梯形則,,

,ω2=,15.945104,(m),,V2=,3.76,(m/s),

,Э2=,2.446,(m),,,,,

,χ2=,12.67,(m),,,,,

,計算兩斷面的平均水力要素如下：,,,,,,,

,ω=,17.28,,,C=,59.9,,

,χ=,15.50,沿途損失能量hf=,,,0.045,(m),

,R=,1.12,,,Э1+iL=,2.492,(m),

,V=,3.47,,,Э2+hf=,2.491,(m),

,因Э1+iL與Э2+hf很相近，說明假設(shè)的h2=,,,,1.652,米是合適的。,,

(二)陡槽計算,,,,,,,,

1求臨界坡降,,,,,,,,

,由A=,0.231,查圖14-19曲線得f(A)=,,0.928,故hk=,1.71,

,其相應(yīng)水力要素為,,,,,,,

,Bk=,11.43,,,Ck=,61.4,,

,ωk=,16.66,,,ik=,0.0027,,

,χk=,12.85,陡槽底坡I=,0.125,＞ik，屬于陡坡。水面線為bⅡ型,,,

,Rk=,1.296,,降水曲線。,,,,

2陡槽長度,,,,,,,,

Ls=,96.75,≈,97,米,,,,

3陡槽水深及水面曲線的繪制,,,,,,,,

假設(shè)h0=,0.543,則相應(yīng)的水力要素為：,,,,,,

,ω0=,4.64,,,C0=,52.2,,

,χ0=,9.54,,,Q0=,60,(m3/s),

,R0=,0.486,求出的Q0與實際流量相等，說明假設(shè)的h0合適。,,,,,

因陡槽前的漸變槽亦為陡坡，故陡槽首端斷面水深hH取為漸變槽末端斷面水深，即,,,,,,,,

hH=,1.652,米。假設(shè)陡槽末端斷面水深接近于正常水深h，故可求出全陡槽,,,,,,

的平均水力要素，即：,,,,,,,,

,h=,1.10,米,,C=,57.8,,

,B=,10.20,米。陡槽段的平均動能變化值j=,,,43.0,,

,ω=,9.98,相應(yīng)于平均水深的流量模數(shù)K=,,,547,,

,χ=,11.10,相應(yīng)于正常水深的流量模數(shù)K0=,,,169,,

,R=,0.899,故水力指數(shù)X=,,,3.34,,

假設(shè)若干水深，按公式（14-2）計算相應(yīng)于這些水深的各斷面之間的距離L：,,,,,,,,

,L=h0/I｛η2-η1-(1-j)〔φ(η2)-φ(η1)〕｝,,,,,,,

h1(m),h2(m),η1,η2,φ(η1),φ(η2),iL/h0,L(m),∑L(m)

1.60,1.200,2.95,2.21,0.035,0.070,0.73,3.16,3.16

1.20,0.900,2.21,1.66,0.070,0.143,2.51,10.91,14.08

0.90,0.700,1.66,1.29,0.143,0.295,6.02,26.17,40.25

0.70,0.585,1.29,1.08,0.295,0.616,13.26,57.62,97.86

,,"計算結(jié)果與陡槽長度L=97米很相近,故陡槽末端水深為0.585米。",,,,,,

4陡槽流速及摻氣水深,,,,,,,,

,,,水面曲線計算成果表,,,,,

斷面,,水深,過水?dāng)嗝娣e,,流速,摻氣高度,摻氣水深,斷面距離

編號,,h(m),ω(m2),,V(m/s),hB(m),h+hB(m),∑L(m)

1,,1.600,15.36,,3.91,0.063,1.663,0.00

2,,1.200,11.04,,5.43,0.065,1.265,3.16

3,,0.900,8.01,,7.49,0.067,0.967,14.08

4,,0.700,6.09,,9.85,0.069,0.769,40.25

5,,0.585,5.02,,11.95,0.070,0.655,97.86

,當(dāng)陡槽中流速大于允許不沖流速時陡槽應(yīng)采取以下措施：,,,,,,,

（1）采用較高的混凝土襯砌；,,,,,,,,

（2）減緩陡槽坡度；,,,,,,,,

（3）當(dāng)流量較小時，可采用人工加糙的措施。,,,,,,,,

(三)消能計算,,,,,,,,

1求第一共軛水深h、和第二共軛水深h＂,,,,,,,,

,取陡槽末端水深為第一共軛水深h、=,,,,0.585,則ξ、=h、/hk=,,0.34

,由公式計算出第二共軛水深,,,h＂=,3.78,h＂/hk=,2.21,≤5故適用

,當(dāng)h＂＞hb(為下游渠道水深)說明在陡槽末端不會立即產(chǎn)生水躍，需要設(shè)置消力池。,,,,,,,

2消力池深度d的計算,,,,,,,,

,下游渠道水深(m)hb=,,,2.00,,,,

,消力池深度(m),,d=σh＂-hb=,2.16,,,,

3消力池長度Lk的計算,,,,,,,,

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因陡槽末端與消力池連接，故可取消力池長度等于水躍長度。,,,,,,,,

,水躍長度的計算：,,,,,,,

,對于梯形斷面渠床，單寬流量可按渠底及水面的平均寬度計算，即,,,,,,,

,q=Q/b+mh=,,,,,,,

,B1、B2為水躍前后兩斷面的水面寬度。,,,,,,,

,,B1=b+2mh、=,,9.17,,,,

,,B2=b+2mh＂=,,15.57,,,,

,水躍長度Ln=5h＂(1+4((B2-B1)/B1)^0.5)=,,,,82.11,米,,

,,故消力池長度取為Lk=,,,82,米